The present invention relates to a method for preparing styryl functionalized silanes, particularly alkoxy silanes. The methods according to the invention resulted in, markedly better yields than those obtained with usual methods.
Styryl-functionalized alkoxy silanes are used in a series of organically polymerizable silicic acid polycondensates which can for example be processed to colored particles (JP Patent 9328624), to oxygen permeable membranes (Y. Kawakami et al., Polymers with oligoorganosiloxane side chains as material for oxygen permeable membranes, Pol. J. 1985, 17, p. 1159 ff), or to electrophotographic materials (U.S. Pat. No. 4,716,091)
However, the preparation of styryl-functionalized silanes is not easy or simple. Kawakami, et al., proposed the preparation of a Grignard compound from styrene followed by a reaction with trichloromethylsilane. The silane compound reacts with the Grignard compound via the chlorine group. However, the product contains further chlorine groups which are highly reactive and either have to be hydrolyzed to hydroxy groups or be subjected to an alternative conversion. In Polym. Comm 26, 133 (1985), the same author describes the preparation of trimethylstyrylsilanes from a Grignard compound and trimethylchlorosilane. The reaction is reported to provide a yield of 36%. (See, Polym J. 17 (11), 1159–1172 (1985)).
The fluorinated styryl alkoxy silanes described in DE 196 13 650 A1 are likewise prepared using Grignard compounds. They can either contain a perfluorinated styryl group or only a perfluorinated phenylene ring. Example 1 provides a detailed description of the preparation of p-vinyl-tetrafluorophenyl-triethoxysilane: a Grignard compound is prepared in situ from perfluorinated bromostyrene and magnesium and reacted with an excess of tetraethoxysilane which is already present in the preparation. The reaction is effected at reflux temperature of diethyl ether. After separation of the magnesium salts and removal of the solvent, the residue is distillated. The synthetic pathway according to DE 196 13 650 A1 can, however, not be transferred to fluorine-free styryl derivates. This is because the formation of the corresponding Grignard reagent from bromostyrene occurs within a considerably shorter time and more exothermally than from the fluorinated derivative. Consequently, an explosive reaction course is to be expected since the Grignard compounds also react exothermally with alkoxy silanes. Moreover, the yield of the styryl-functionalized alkoxy silane obtained by this reaction is only 35%. Such a yield is unsatisfactory.